KR100330818B1 - Polyester films containing precipitated silica particles and calcined china clay - Google Patents

Abstract

The present invention relates to films or sheets of linear polyester having incorporated therein a combination of precipitated silica particles and calcined clay having certain particle sizes and present in specific amounts based upon the weight of the polyester film. The addition of these fillers improves several properties of the film, including the handleability while maintaining acceptable optical clarity and transparency and to the method of making such films or sheets.

Description

Polyester film containing precipitated silica particles and calcined clay {POLYESTER FILMS CONTAINING PRECIPITATED SILICA PARTICLES AND CALCINED CHINA CLAY}

The present invention relates to polymer films, in particular polymer films with blends of fillers and methods of making such films.

Films or sheets of linear polyester have been commercially available for many years.

Polymeric films have excellent stretch orientation and are particularly suitable for biaxial film orientation processes to provide films with excellent properties. Polymer films known as polyethylene terephthalate or PET are strong and have excellent inherent chemical and thermal stability.

Polymer manufacturing and film processing processes are known to those skilled in the art and include the literature (Encyclopedia of Polymer Science and Engineering, 2nd Ed, vol. 12, John Wiley and Sons, Inc ,, pages 1-313) and numerous US and foreign patents. It is also described in numerous documents.

Polymer films are known to be poorly handled, making it difficult to wind the film onto a high quality reel and sometimes not to pass efficiently through processing equipment such as slitting machines. Film handling properties can be improved by suitably increasing the surface roughness of the film by using a coating or optionally incorporating fillers such as organic and inorganic particles into the film. Combinations of coatings and fillers can be used to improve film handling properties. The use of coatings to improve the handling properties of the film limits the use of the film because it is difficult to apply additional coating layers that may be necessary, for example, to impart antistatic, adhesion promoting or release properties. have.

Various fillers may be incorporated into the film to improve the handling properties of the film. For example, glass spheres and fumed silicas described in US Pat. Nos. 5,132,356 and 5,137,939: Synthetic silica, calcium borate, calcium carbonate, magnesium carbonate, barium sulfate, calcium silicate as described in US Pat. No. 4,274,025. Or inorganic materials including aluminum silicate and glass spheres. While these fillers provide performance improvements, generally films containing these fillers are limited to specific applications.

Incorporating a small amount of particulate filler into the film presents a number of problems, particularly when processing polymers. Generally, the filler is preferably added to the resin system before polymerization. However, in this case, the filler is exposed to the polymerization reaction and related reaction conditions, so another filler performance should be considered. The filler may react, decompose and coagulate under process conditions such as heat, time, stirring and pressure necessary to complete the polymerization. Thus, the processing properties of the filler can cause numerous processing problems.

For various film applications such as packaging, metallized films, copy films and general industrial films, optical transparency and transmittance are important. There is a continuing need for films with high light transmittance, low haze and excellent handling properties and more common fillers in use and processability. Moreover, in recent years there has been a strong demand for films that include filler systems that do not scratch the surface well when in close contact with two or more layers of such films.

The present invention surprisingly overcomes or substantially reduces one or more of the above mentioned problems.

Accordingly, the present invention provides a polyester film having excellent handling properties, including improved anti-blocking and reduced crises, pimpling and machine direction (MD) wrinkles.

In a second aspect of the present invention there is provided a film comprising filler particles that have been softened to such an extent that the surface of the adjacent layer of the film is not scratched when the film is processed or eventually used.

In the third aspect of the present invention, there is provided a polyester film which is not only excellent in handling characteristics but also low in blur and good in optical transparency.

In the fourth aspect of the present invention, there is provided a polyester film incorporating a blend of fillers having good processing characteristics.

In a fifth aspect of the present invention there is provided a polyester film incorporating a blend of fillers that do not react, decompose or agglomerate when exposed to polymerization reactions and reaction conditions.

The present invention relates to a film or sheet of linear polyester in which a blend of precipitated silica and calcined clay of a particular particle size is incorporated in a specific amount based on the weight of the polyester film and a process for producing such a sheet or film. By adding these fillers it is possible to improve some properties of the film, including handling properties, while maintaining acceptable optical transparency and transmittance.

The present invention is a combination of (a) precipitated silica particles of less than 15 microns in average particle size present in an amount of 25 to 500 ppm by weight of polymer and (b) calcined clay present in an amount of 10,000 ppm or less by weight of polymer. It relates to a polyester film containing the incorporated polyester polymer

Precipitated silica particles useful in the practice of the present invention include SiO ₂ and may or may not be modified. Such silica particles can be modified with various techniques, processes and compounds, especially those that make the particles more hydrophobic. Preferred precipitated silica particles are those sold under the trade name SYLOID by WR Grace.

Precipitated silila particles used in the present invention generally have an average particle size of 1 to 10 microns, more generally 2 to 8 microns. Precipitated silica particles are present in small amounts of 30 to 350 ppm by weight, preferably 50 to 250 ppm by weight and most preferably 100 to 200 ppm by weight, based on the polymer weight.

Calcined clay useful in the present invention can be produced by processing ordinary hydrous clay. One of the common methods for preparing calcined clay is as follows; First, dry milling the hydrous clay, pneumatic classification and purification, exposing the clay to 1000 ° C. or higher, firing it, and then milling it in water for subsequent processing and finally azeotropic distillation to remove the water to remove the ethylene glycol slurry. Manufacture.

A given sample of calcined clay shows an average particle size micron of at least about 50% of the particles as measured by a conventional particle size analyzer. The calcined clay of the present invention has an average particle size of 1 micron or less, preferably 0.85 micron or less, most preferably 0.25 to 0.75 micron or less, preferably 0.85 micron or less, and most preferably 0.25 to 0.75 micron. Calcined clay is introduced into the polymer in an ethylene glycol slurry comprising up to 55 weight percent solids, typically up to 50 weight percent solids, based on the total weight of the slurry. A preferred calcined clay slurry is the trade name InFilm 3117 (English China Clay International), which has a mean particle size of 0.3 microns measured by a Microtrac Model II-particle size analyzer, a particle size distribution of 98% for 2 microns or less and 90% for 0.5 microns or less. Having a product.

The amount of calcined clay present in the polyester film is 10,000 ppm or less, generally 8,000 ppm or less, preferably 1000 to 5000 ppm by weight, based on the polymer weight of the polyester film.

The required amount of precipitated silica particles and calcined clay may be added to the polyester film forming polymer at any instant in the film making process prior to extruding the polymer.

In general practice of the present invention, it is preferred to incorporate precipitated silica and calcined clay particles into the polyester during the polymerization production of the polyester. A common procedure is to add the particles to the polycondensation mixture used to prepare the polyester. It has been found to be particularly preferred to add these particles as a slurry after transesterification in which monomers are formed in the production of polyester films. For example, the particles can be added as a slurry in glycol that forms a polymer film before initiation of the polycondensation reaction.

Polymers useful in the manufacture of the inventive films are known to those skilled in the art and can be obtained from any film forming polymeric material. One or more dicarboxylic acids or their lower alkyl (C ₆ or lower) diesters such as terephthalic acid, isophthalic acid, phthalic acid, 2.5-, 2,6- or 2,7-naphthalene dicarboxylic acid, succinic acid, sebacic acid, ac One or more glycols with diflic acid, azelaic acid, 4,4'-diphenyl dicarboxylic acid, hexahydro terephthalic acid or 1,2-bis-p-carboxy-phenoxyethane (with any monocarboxylic acid such as any pivalic acid) In particular, synthetic linear polyester polymers obtainable by condensation of ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol are particularly effective for the production of films of the invention. It turned out. Polyethylene terephthalate films are particularly preferred, in particular biaxially oriented at a temperature of 70-125 ° C., as described in British Patent 838,708, and preferably heat-set at a temperature of 150-250 ° C. in general.

The polyester film prepared from the composition according to the present invention may be uniaxially or biaxially oriented, but is preferably biaxially oriented so that the blending of mechanical and physical properties is satisfactory by stretching in two directions perpendicular to each other in the film plane. Preferably, the film is biaxially oriented by sequentially stretching in two directions perpendicular to each other at a temperature of 70-150 ° C.

Such stretching methods are described in numerous patents, including British Patent 838,708. These techniques are known to those skilled in the art of polyester film production.

The polyester film of the present invention is generally formed to a thickness of 175 microns or less, more generally 100 microns or less, preferably 50 microns or less, most preferably 9 to 25 microns or less.

Conventional coating media can optionally be applied to one or both sides of the polyester film of the present invention. Such coatings are conventionally added to enhance adhesion or antistatic properties. The chemical composition of these coatings is known to those skilled in the art and is described in numerous patents and publications. The coating medium may be applied to the uniaxially or biaxially oriented film substrate. In the simultaneous biaxially oriented stretching process, the coating medium may be suitably applied to the substrate before or after completion of the stretching operation. In the sequential biaxially oriented stretching process, it is preferable to apply the coating medium to the film substrate between the two stretching stages, ie, between the longitudinal and transverse stretching stages of the biaxial stretching operation. This stretching and coating sequence is particularly preferred for producing coated polyethylene terephthalate films. It is preferred that the film is drawn longitudinally on a series of rotary rollers, then coated with a coating medium, finally stretched transversely in a stenter oven and then heat set the coated film.

Any coating medium may be applied to the polyester film by any conventional coating method such as dip coating, bead coating, gravure, reverse roller coating or slot coating as an aqueous dispersion or organic solvent solution.

The temperature applied to the coated film upon subsequent stretching and / or heat setting is effective for drying the solvent in the case of an aqueous medium or solvent application composition, and is effective for coalescing and for the coating to form a continuous and uniform layer.

Any coating layer may be applied to one or both sides of the polyester substrate and one or both sides of the coating layer may be coated with additional material. Thus, the function of the coating layer may be a sublayer to aid subsequent deposition of additional coating layer (s) or a coating to improve the handling properties of the film.

The one or more polymer layers and optional coating layers of the polyester film substrates used in the preparation of the composition may contain any additives commonly used in preparing thermoplastic polyester films. Thus, if necessary, additives such as dyes, pigments, foaming agents, lubricants, antioxidants, antiblocking agents, surfactants, slip agents, gloss enhancers, predegradants, UV stabilizers, viscosity modifiers, dispersion stabilizers, fillers and filler blends are required. And / or in the coating layer (s).

The invention will be more readily understood by reference to the following examples which show some embodiments of the invention.

<Example>

The following materials and test procedures were used in this example:

SYLOID-74: Precipitated silica particles having an average particle size of 7 to 8 microns (manufactured by W.R. Grace Inc.).

SYLOID-150: Precipitated silica particles with an average particle size of 2.0 microns (manufactured by W.R. Grace Inc.).

SYLOID-F150: Precipitated silica particles with an average particle size of 2.1 microns (manufactured by W.R. Grace Inc.).

SYLOID-234: Precipitated silica particles having an average particle size of 2.5 microns (manufactured by W.R. Grace Inc.).

SYLOID-235: Precipitated silica particles with an average particle size of 4.0 microns (manufactured by W.R. Grace Inc.).

Filler Concentrations: Unless otherwise noted, all filler concentrations are given in ppm by weight of polymer.

Average particle size: All units of average particle size are in microns and measured with a Microtrac Model II-particle size analyzer

Blur%: measured with Gardner Hazemeter

MD grade: A measure of the winding properties of a film, at least 4,572 m (15,000 ft) of film was wound on the core at a high speed of about 549 m (1800 ft / min), and then the width of the increased film line was measured. The quality of the film was evaluated by dividing the sum of these lines by the total width of the film and normalizing them to grades 1-10 (1 means that the visible line is zero).

Speckle rating: A measure of the optical quality of the film surface, the deformation of the light reflected from the metallized surface of the film, was observed to indicate when there was almost no speckle.

<Example 1>

Into a 94.64 L (25 gallon) Ross mixer was added 37.85 L (10 gallon) of ethylene glycol with stirring followed by 0.284 kg of SYLOID-74. With constant stirring, the average particle size as measured by the Microtrac Model II-particle size analyzer is about 0.3 microns, and the particle size distribution is about 6.82 containing about 51% solids in ethylene glycol with 98% for 2 microns or less and 90% for 0.5 microns or less. kg of calcined clay slurry (trade name InFilm 3117, available from English China Clay International) were added. Bishydroxyethylene terephthalate (monomer) was prepared by reacting about 2100 L of dimethyl terephthalate (DMT) with 1260 L of ethylene glycol in a separation vessel at about 220 ° C. The mixed filler slurry was mixed for about 1 hour and then pumped into the monomer with constant stirring. The temperature of the monomer composition was then raised to about 240 ° C. and stirring continued for approximately 10 minutes until substantially all excess ethylene glycol was removed.

After the monomer / mixed filler composition was placed in a conventional autoclave, the molten monomer was polymerized under stirring at about 285-290 ° C., about 53.33 Pas (about 0.4 mmHg).

The resulting polyethylene terephthalate was cooled to room temperature and then converted to chip form with a conventional pelletizer.

The dried chips are extruded into a film at about 285 ° C. using a conventional film manufacturing apparatus, and then biaxially oriented by sequentially stretching them in two directions perpendicular to each other using a conventional apparatus such that the draw ratio is about 3.1: 1. Thermal curing at about 220 ℃.

The resulting fill film product had a total thickness of about 12 microns and a haze of about 3.6% as measured by Gardner Hazemeter. In addition, the optical transparency was good, and as a result of evaluating the winding property by fast winding a film of about 6096 m (20,000 ft) or more on the core at a linear speed of about 549 m (about 1800 ft / min), the outer surface of the wound film was evaluated. Blocking pimples were rarely observed in, and there were no MD wrinkles or crises.

Examples 2-7

Examples 2 to 7 Filled according to the procedure of Example 1 with varying amounts and particle sizes and the results are summarized in Table 1. Table 1 also shows the results of the evaluation of the flow chart%, machine direction line grade and speckle grade of these films.

<Table 1>

Claims (9)

A blend of (a) precipitated silica particles of less than 15 microns in average particle size present in an amount ranging from 25 to 500 ppm by weight of polymer and (b) calcined clay present in an amount of up to 10,000 ppm by weight of polymer. Polyester film containing the polyester polymer which mixed. The film of claim 1 wherein the calcined clay has an average particle size of less than 1 micron. The film of claim 2, wherein the calcined clay is present in an amount of less than 8,000 ppm by weight based on the polymer weight. The film of claim 1, wherein the average particle size of the precipitated silica particles is from 1 to 8 microns. The film of claim 4, wherein the precipitated silica particles are present in an amount of 50 to 300 ppm by weight, based on the polymer weight. The film of claim 1, wherein the film thickness is less than 50 microns. (a) an average particle size of from 2 to 8 microns of precipitated silica particles present in an amount ranging from 50 to 250 ppm by weight based on the polymer weight and (b) an average present in an amount ranging from 1,000 to 5,000 ppm by weight based on the polymer weight. A polyester film comprising a polyethylene terephthalate polymer incorporating a blend of calcined clay having a particle size of 0.25 to 0.75 microns. 8. The film of claim 7, wherein the calcined clay has an average particle size of 0.3 microns and a particle size distribution of less than 2 microns 98% and less than 0.5 microns 90%. (a) precipitated silica particles of less than 15 microns in average particle size present in amounts ranging from 25 to 500 ppm by weight of polymer, and (b) calcined clay present in amounts of up to 10,000 ppm by weight of polymer. A polyester film comprising a polyester polymer incorporating a blend, wherein one or both surfaces are coated with a coating layer.